Subjects in a Physical World

I. Introduction

Philosophy of mind today reaches into almost every area of philosophy and many other fields of research outside philosophy. At the very heart of philosophy of mind is what traditionally has been called the ‘mind-body problem’.

The mind-body problem can be framed by listing three assumptions we take for granted in our everyday life. These are:

  1. The world we live in is material. There are atoms, tables, cats and human beings and all of them are made out of basic material particles.
  2. There is mental life. When we think, imagine or feel we engage in mental activities.
  3. The mental seems to be different from the physical. The mental activities we engage in have properties that are not ascribed to material entities.

In our every day life we naturally presume that the world is material and at the same time that we have a vivid mental life. What we probably do not reflect on more precisely is how the physical world and our mental life are related to each other, thus how these three assumptions can be put together consistently. Reflecting about how this can be done starts the conundrum troubling philosophers ever since: If there is mental life and the physical realm, what is their relation? Is the physical identical to the mental or altogether different? If the mental ought to be distinguished from the physical, how is causal interaction among them possible? These questions dominate contemporary debates in philosophy of mind.

II. Reductive and non-reductive physicalism

One strategy to solve the mind-body problem is reductionism. It assumes that the mental life we engage in is identical with brain processes. We are nothing over and above our brain and all our thoughts and feelings are ultimately identical with physical properties (e.g. Heil 2003, Kim 2005).

In his classical paper on reductive physicalism J.J. Smart openly confesses: “It seems to me that science is increasingly giving us a viewpoint whereby organisms are able to be seen as physiochemical mechanisms […] A man is a vast arrangement of physical particles, but there are not, over and above this, sensations or states of consciousness.” (Smart 1959/2004, 117-118).

A major problem reductive physicalism faces is that so far it has been unable to cash out practically the strategy of reduction it proposes. On a first view it seems intuitively appealing to suppose that everything is physical – our mental life included. If everything else is physical don’t we have to assume that the mental is ultimately physical too? For if it isn’t, mental life would amount to a “nomological dangler” which we do not know how to integrate in our physical world. From a reductive physicalist point of view this situation is doubtlessly unsatisfactory. Practical arguments based on the principles of parsimony and simplicity seem to decide overwhelmingly in favour of a theory postulating the identity of mental life with brain processes (see Smart 1959/2004, 127).

The course of philosophical discussion, however, has not vindicated Smart’s view. It seems impossible to reduce phenomena such as sensations, emotions and our first-person perspective to the physical. It still hasn’t been explained how the experience of pain, for instance, can be reduced to a certain neuronal state of our brain (such as the famous C-fibre firing). The resistance of mental phenomena to reduction seems to be insurmountable.

In the light of the pertinacious problems reductionist strategies face, reductive physicalism has lost much of its convincing force. Thus, non-reductive physicalism evolved as an alternative. It claims to be able to combine all the three assumptions listed above. According to non-reductive physicalism, the world we live in is physical and we are physical parts of it. Nevertheless, we are able to think, feel and imagine whereby these capacities are not identical with physical processes.

Lynne Rudder Baker recently put forward a non-reductive physicalist account (Baker 2008). She sums up her view as follows: “Proponents of nonreductive materialism hold that the mental is ontologically part of the material world; yet, mental properties are causally efficacious without being reducible to physical properties.” (Baker 2008, 1) She identifies three basic assumptions that minimally characterize non-reductive physicalism:

  1. The first thesis we call the “distinction thesis”. Baker describes it as follows: “There are mental properties such as pain, sensations and the like that are distinct from any physical properties.” (Baker 2008, 2) This thesis basically characterizes property dualism, which says that mental properties are not reducible to the physical realm. However, this thesis standing alone would be compatible with substance dualism as well, so that a further elaboration of non-reductive physicalism is needed.
  2. Therefore, Baker adds a second thesis which we call the “dependency thesis”. Mental properties depend on physical properties (Baker 2008, 3). The “dependency thesis” implies strong dependency in the sense that no change in mental properties is possible without change in the physical basis.
  3. The third thesis of Baker’s definition of non-reductive physicalism is the “causality thesis”: “Finally, nonreductive materialists eschew epiphenomenalism about mental properties: mental properties make a causal difference [...].” (Baker 2008, 3) Mental properties have causal powers and contribute to what happens in the world.

Central for Baker’s account is that mental properties are not reducible to physical properties although we ware physical beings (Baker 2008, 4-8). In her discussion of non-reductive physicalism Baker focuses on what she calls “intention-dependent-properties”: These are properties that cannot be instantiated in a world without beings endowed intentionality. Take, for instance being in debt, being a driver’s licence or being a delegate. Nobody can be in debt and nothing can be a driver’s license in a world lacking beings with intentionality (Baker 2008, 12). According to Baker’s argument it is highly unlikely that ID-properties are reducible to physical properties invoking no reference to intentionality at all.

Whether Baker succeeds in defending a tenable version of non-reductive physicalism others shall decide. We use Baker’s characterization of non-reductive physicalism as paradigm to point out what motives stay behind non-reductive arguments:

Non-reductive physicalism advocates the irreducibility of mental properties for we need to be realists about them if we want to be realists about a world where president’s are elected, financial budgets are cut down, couple get married and people care about pain, sorrow or joy. However, non-reductive physicalism opposes substance dualism, understood as the view that not only some of our activities but people themselves are irreducibly mental. Even though we have irreducible mental properties, we are still physical beings.

It is important to notice that non-reductive physicalism endorses property dualism: Claiming that our mental life is irreducibly different from physical entities and contributes causally to what is going on in the world commits one to the existence of mental properties: ”The irreducibility of conscious experience and self-determining action we affirmed at the outset already commits one to a kind of dualism, a duality of physical and conscious properties.” (O'Connor 2003, 4)

It is this commitment to a version of dualism which makes the weak point of non-reductive physicalism apparent. For even though it doesn’t invoke any kind of immaterial substances, there are at least irreducible non-physical properties. Non-reductive physicalism isn’t more parsimonious, ontologically speaking, than substance dualism: It leads to a division of the universe into two different realms, one physical and one mental. The causal relationship between mental properties and physical entities is in need of explanation, if substance dualism’s interactionism is. Non-reductive physicalism conceived as property dualism is simply too close to substance dualism to have any advantages over it. If these brief considerations are sound, then these are serious problems for non-reductive physicalists. For if there is no reason to favour non-reductive physicalism over substance dualism, then anyone with physicalist tendencies better returns to reductive physicalism.

This, however, is just the first part of the story. Non-reductive physicalists have to answer a further question, namely what it means to have mental properties. In what fallows we argue that once irreducible mental properties are accepted and once we have realized what it means to have mental properties, then substance dualism is a much more viable position in philosophy of mind as it is generally assumed. Non-reductive physicalism on the other hand looses further credibility.

III. Characterizing the mental

First we need to take a closer look on the defining characteristic of mental properties, namely what we call their “subjectivity”: While everything physical is objectively accessible every mental property is essentially subjective: It can only be grasped from a certain subjective persspective. What it is like for someone to be in a certain mental state cannot be grasped from a third person perspective (Nagel 1986), there is no impersonal way of experiencing (Kim 1995, 162). It is this “What it is like”-character of mental properties which makes them such a queer object for scientific investigation: While science can tell us what goes on in our brains when we have, say, a certain impression of red it cannot grasp what it is like for us to have this impression of red. This phenomenal character of mental properties called ‘quale’, plural ‘qualia’, is inaccessible to science.

Probably the most illustrative case of working out what qualia are about is Frank Jacksons thought experiment about Mary, a brilliant colour scientist (Jackson 1986). Mary, so the story goes, is the leading scientific authority on colours. She knows every scientific fact there is to know about colours, colour vision and neuronal processing of colour impressions. However, Mary is imprisoned in a white and black room and all the objects she has ever had contact with are black and white as well. Although knowing everything about colours, Mary has never seen colours. The question now is whether Mary comes to know something new when she leaves the room and sees a coloured object for the first time in her life.

What is important to note is that the thought experiment about Mary does not imply belief in qualia in terms of inner mental objects which are inaccessible from the outside. The point, according to Anthony Rudd (1998) is not to postulate controversial objects which apparently cannot be integrated into a physicalist framework. A quale is not a bare phenomenal property which adheres to an object or which can by analyzed independently of our interpretations of the object it supposedly adheres. To think in terms of qualia as mental objects which are “detected” exclusively from our subjective perspective is to aim at objectivising what essentially is subjective. Chalmers, for instance, distinguishes two classes of mental states, “psychological” and “phenomenal” states. Psychological states are states playing the right kind of causal role for bringing about behaviour and include beliefs, desires, perception and memory. Phenomenal states instead are states with a qualitative character, states such that there is “something it is like” to be in those states, like pain, visual experiences of colours or olfactory experiences of smells (Chalmers 1996, 11).

According to our understanding of Jackson’s Mary-argument Chalmer’s considerations are based on false assumptions. What the Mary-argument, understood properly, really points out is that we have experiences, e.g. of seeing red, access a additional instrinsic property of a representational state. The question whether Mary comes to know somethingnew – phenomenal states – is ultimately a red herring. The fundamental problem for physicalism is not that some states of mind represent non-physical phenomenal objects but that the notion of experience itself cannot be cashed out in physical terms (Rudd 1998). What Mary lacks is, “not acquaintance with some special inner object of awareness – coloured sense-impressions, or something of the sort – but simply acquaintance with anything we can see, ordinarily visible objects in the world. […] The aim of the argument is, not to focus on some inner mental object of awareness, but on awareness itself” (Madell 1988, 85).

If people like Chalmers try to dissect “psychological states” from “phenomenal states”, then two mistakes are made. First, the phenomenal is reified. As pointed out, the main thrust of qualia-arguments such as Jackson’s is to underline that our mental life has something ineliminable subjective. The discussion about the phenomenal is not primarily a discussion about knowledge and entities known or unknown but it is a discussion about what it is like to be aware of something. Second, dissecting the phenomenal from the psychological creates the impression that only certain “bits of our mental life” are phenomenal whereas the rest is psychological but not phenomenal (Chalmers 1995/2004, 617-619). Because psychological states can be functionalized, such a move fuels once again attempts to reduce at least the psychological. We end up with a form of non-reductive physicalism which is almost entirely reductive: only the postulated intrinsic qualitative properties of our mental life resist reduction (for such an account see Kim 2005, 165-174). If our characterization of the mental is sound, instead, distinctions such as the one between the phenomenal and the psychological might be useful for certain purposes but they are definitely misleading for understanding the mental.

Characterizing the mental as essentially subjective does not mean, however, that we are solipsisticly “locked” into our minds and that there is no intersubjective way of talking about the mental. Objectivity in the ascription of mental states, however, can only be achieved in a community of persons who are all disposed to experience these mental states. All I can do to understand your behaviour is to project my own experience of, say, pain onto you. Thereby, only because I know what its like for me to be in pain, I can imagine what it is like for you to be in this subjective state as well. I can observe another person and her expression of being in pain but I cannot observe what it is like for her to be in pain. Often the mental states we experience find a natural and immediate expression in and through the behaviour we can observe. It would be ill-conceived to assume that mental states are the causes of the behaviour in such a way that first the mental states take place which causally produce a subsequent corresponding behaviour. The relation between mental states and expressive behavior is an internal, not a causal one. Normally when someone is in pain, his feeling of pain finds a natural expression in certain forms of behaviour. For this reason our own and someone else’s mental lives are not irrevocably hidden from us. We have a limited access to the other’s state of mind in her gestures, mimic, deportm nt etc. If science describes bodily behavior from an impersonal point of view in terms of physical processes, then such a description is the result of abstracting from our primarily personal and social understanding of the human behaviour.

IV. Bearers of the mental

A basic metaphysical claim is that properties need bearers or substances to exist: The green of the grass couldn’t exist if the grass didn’t exist and so on. There are no properties floating free. Let us ask then: What are plausibly the bearers of mental properties? Can we make sense of the non-reductive physicalist’s claim that brains or biological organisms are bearers of mental properties? If mental properties are defined by their functional role, then a brain or a biological organism as a whole might plausible count as a bearer of the mental. Such a conception of the mental, however, does not account for its essentially subjective character. Mental properties need to be experienced by their bearers to exist – in contrast to physical properties whose existence does not depend on anyone experiencing them. Thus, our first question about possible bearers of the mental needs to be readdressed in the following way: Can a brain or – generally speaking – a physical entity be a subject of experience as non-reductive physicalism assumes?

Saying that mental properties are essentially subjective implies that mental properties are not reducible to physical properties conceivable from an objective point of view. Pain, for instance, is not reducible to certain neuronal patterns for the subjective experience of pain is different from neuronal facts involving certain regions in the brain and the nervous system. This taken for granted, the question arises which objective criteria we can draw upon for deciding which physical entities are subjects of experience. If physical states like neuron firings are not identical to mental states such as experiencing pain, then it is unclear how it can be argued for the thesis that a physical object like the brain is the subject experiences presuppose. To put it differently: If pain cannot adequately be characterized as physical state, how can we think of it as actually being experienced by a physical being?

Non-reductive physicalists are inclined to think that physical objects such as brains, nervous systems or sense organs are plausible candidates for being subjects of experience whereas stones, tables and skyscrapers are not. The plausibility of this claim is based on the intuition that nervous systems, brains or sense organs are causally responsible for bringing about our mental life while stones, tables or skyscrapers are not entities staying in any relation to mental life. It is uncontroversial that a physical object like the brain is processing physical states like neuron firings. The long cultural history of drug (ab)use is a lucid example that people were aware for centuries of a close relation between brain and mind. It was no secret that influencing the brain via toxic substances has proven highly successful for influencing the mind. Thus, it can be argued, knowledge about how specific brain processes work helps to understand specific mental states (Searle 1992, 100-104). Whether mental properties are causally generated by the brain or not is not in question. The generation of mental life is not to be conflated with the experience of mental properties. What is at stake is the claim that the brain is actually experiencing pain, joy, sorrow etc.

If a causal account cannot help to identify the bearers of mental states, then it is hard to see which other criteria can be brought forward for the thesis that physical entities are bearers of mental life. If there is nothing that could make it objectively true that it is the brain which is a subject experiencing mental properties than we have reason to assume that any other physical object is a subject of experience (see Foster 1991, 209-211, for a succinct discussion of this argument). Thus, the question which physical object is a subject of experience amounts to a matter of mere stipulation. In the light of this argument it is plausible to assume that similar to the mental states experienced subjects of experience are not part of the physical realm either. The bearers of mental properties – the subjects experiencing them – are mental too. We conclude that we are embodied mental substances. To argue for mental substances is to argue for substance dualism. If we conceive ourselves as mental substances we are in the best position to make sense of our peculiar and irreducible subjectivity.

V. Substance dualism in the interdisciplinary dialogue

It is time to sum up: We argue that once it is accepted that mental properties are irreducibly subjective and thus cannot be identified with physical properties one has to bite the bullet and become a substance dualist. Substance dualism seems to be the only tenable position left, once thorough reductionism of the mental is rejected. Non-reductive physicalism does not have any advantages over dualism. Additionally, however, it has to explain how physical entities can be bearers of genuinely non-physical properties. Embodied substance dualism, as advocated in this paper, doesn’t presuppose soul-bubbles (Dennett 1991, 423) or mental stuff. Neither do we claim that mental substances are somehow added to a material body, for instance through divine interaction, nor are subjects of experience hidden in a body or ensnared in it. The substance dualist can endorse the view that subjects of experience, though not physical beings, express themselves via their organisms, out of which they emerge (Taliaferro 2001, 66). It is excluded that a mental substance can naturally leave the physical system out of which it emerges and switch to another one. On the contrary, we are in a deep interrelationship and, even more, in a peculiar unity with our body (Taliaferro, 1994, 114-122). However, this intimate relationship doesn’t render our bodies or brains subjects of experience. A functioning brain and organism is certainly a necessary material condition for a subject’s existence but the brain cannot be a subject experiencing anything.

What our view of substance dualism excludes is that subjects experiencing the world can be fully captured with the methods of science. But this should not be considered as an affront against science. There is nothing anti-scientific about the version of dualism we are advocating. Neuro-psychology, for instance, is no contradiction in terms. It tells us facts about the physiological processes underlying our thoughts, feelings and experiences. Of course, changes in the organism or brain do cause changes in the mental life of the subject which emerges from it. What we do stress, however, is that there is more to reality than science can tell us. It is important to underline at this point that more data, better construed scientific models or more agreement among scientists cannot solve the problem of the mental. For the difference between reductive or non-reductive physicalism and dualism is not a question concerning scientific facts but a question of how we understand the project of explaining what mentality is (Moreland&Rae 2000, 41-43). Physicalists are trying to explain what mentality is within current scientific frameworks. Dualism, as we presented it, has its primary focus on the subjectivity of the mental instead, which doesn’t fit into a scientific and therefore third-personal framework.

This view has consequences for the relationship between science and philosophical anthropology. It is often said that there is empirical support for physicalism and against dualism (for instance Murphy 1998, 140). It seems to us that such a line of argumentation is changing the subject: The philosophically interesting phenomena, such as experiential features of our mental life, its subjectivity or the question of what kind of entities the bearers of such a mental life might be are issues science cannot settle at all.

We have argued for substance dualism on purely philosophical grounds. Without doubt many religious thinkers show a natural affinity to dualist thinking. Prominent thinkers favouring dualism write from an explicitly Christian viewpoint (e.g. Swinburne 1986, Cooper 1989/2000, Moreland&Rae 2000, Plantinga 2007). If indeed there are compelling philosophical arguments for substance dualism, then an affinity towards dualism from a Theistic worldview is rationally vindicated.



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